1. Field of the Invention
This invention pertains generally to the field of aircraft display units that present information to the pilot of an aircraft.
2. Description the Related Art
A visual situation display (“VSD”) or a vertical profile display is known to those skilled in the art to provide a side view or profile of the vertical flight path of an aircraft. Along with the vertical flight path, features such as waypoints, airports, runways, and/or terrain are presented within a grid measured by vertical and horizontal scales. The vertical scale may provide altitude information of the flight path, and the horizontal scale may provide distance or time information. A horizontal scale providing distance information has been disclosed by Chen et al in U.S. Pat. No. 6,995,690 entitled “Vertical Situation Display Terrain/Waypoint Swath, Range to Target Speed, and Blended Airplane Reference,” and a horizontal scale providing time information has been disclosed by Barber et al in U.S. Pat. No. 8,099,201 entitled “Vertical Profile Display with Enhanced Temporal Depiction of Navigation Information.” As disclosed by both Chen and Barber, the information provided in the VSD is typically limited to a swath of area corresponding to the flight path. Features such as waypoints and terrain located within the swath are included in the VSD, and those located outside of the swath are not.
When a feature leaves the area of the swath, the VSD symbol representing the feature may suddenly disappear from the VSD as it crosses a boundary of the swath; similarly, when a feature moves into the area of the swath, the feature may suddenly appear on the VSD. Because the edges of the swath may depend upon the location of the flight path, momentary diversions of the aircraft from the flight path could cause the VSD symbol to flicker (i.e., suddenly appear and disappear or vice versa) as the feature momentarily enters or leaves the swath. Because this flickering may be a source of a nuisance and annoying to the pilot, an unwanted distraction may arise which diminishes a pilot's situational awareness and/or concentration as he or she accomplishes other tasks related to flying the aircraft.